type_intern.rs

use std::{collections::HashSet, rc::Rc};

#[derive(Debug, PartialEq, Eq, Hash)]
pub enum Type {
    Int,
    String,
    Boolean,
    Array(Box<Type>),
    Function(Vec<Type>, Box<Type>), // parameter types, return type
}

#[derive(Default)]
pub struct TypeInterner {
    types: HashSet<Rc<Type>>,
}

impl TypeInterner {
    pub fn new() -> Self {
        Self {
            types: HashSet::new(),
        }
    }

    pub fn intern(&mut self, t: Type) -> Rc<Type> {
        if let Some(existing) = self.types.get(&t) {
            existing.clone()
        } else {
            let rc_type = Rc::new(t);
            self.types.insert(rc_type.clone());
            rc_type
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_intern() {
        let mut interner = TypeInterner::new();
        let t1 = interner.intern(Type::Int);
        let t2 = interner.intern(Type::Int);
        assert_eq!(t1, t2);

        let t3 = interner.intern(Type::String);
        assert_ne!(t1, t3);

        let t4 = interner.intern(Type::Array(Box::new(Type::Int)));
        assert_ne!(t1, t4);

        let t5 = interner.intern(Type::Array(Box::new(Type::Int)));
        assert_eq!(t4, t5);
    }
}